Apparatus for use in combination or in conjunction with alpha sextant adapted for useas an artificial horizon and direction indicator



M y 10, 1932- O L. H. MORRISON 7,736. APPARATUS FOR USE INCOMBINATION OR IN CONJUNCTION WITH A SEXTANT ADAPTED 7 FOR USE AS AN ARTIFICIAL HORIZON AND DIRECTION INDICATOR Y Filed June 27, 1929 5 Sheets-Sheet l y 1932- H. MORRISON 1,857,736

APPARATUS FOR USE IN COMBINATION OR IN CONJUNCTION WITH A SEXTANT ADAPTED FOR USE AS AN ARTIFICIAL HORIZON AND DIRECTION INDICATOR Filed June 27, 1929 3 Sheets-Sheet 2 May 10, 1932. MoRRlsol'yi' 1,857,736 A APPARATUS FOR USE IN COMBINATION OR IN CONJUNCTION WITH A SEXTANT ADAPTED FOR USE AS AN ARTIFICIAL HORIZON AND DIRECTION INDICATOR Filed June.27, 1929 '3 Sheets-Sheet 3 3/ {66 s I I w 1 9/4 26 Pus n an 10, '19s oNiTsn' v STATES PA ENT OFFICE. Q 'l nauamrcn may nonmson, or onnvssnnn, ENGLAND srrm'rus For. use IN commsrron on IN conmno'rxon WITH A snxrsn'r I son USE AS AN ARTHICIAL HORIZON AND nmno'rron mnros'ron Application filed June 27,1929, Serial no. 374,159, and in Great Britain July 24, 1928.

This invention relates to apparatus adapted to be used in conjunction or in combination with a sextant, and has. for itsobject to rovide'improved means whereby an arti cial' horizon is formed and the direction of .an Ob,

served body is indicated to an observer at the time of an observation; Bythis means, vertical angles extending from the zenith to below the natural horizon can be measured, and the vertical plane of direction through the observer and the observed body can be shown without the need of further observation or inspection of nautical tables.

"Among other obiects and advantages the invention seeks to provide (1) An-o'ptical'device which presents an artificial horizon line, the artificial horizon bein the reflected image of a horizontal line whifil is fixed relativelyto the point'of observation,'hereinafter referred to. J

' (2) An arrangement whereby the means of reflection, ab'ove referred to, is stabilized against disturbing influences suchas arise from the rolling and pitching motions of a ship at sea. I

, (3) Means whereby direction is indicated to an observer at the time of an observation.

' Witha view .to'the clear understanding of the invention, each principle will now be ex plained in greater detail; and whilst explainmg, Figures 1 and 2 will be referred to as occasion demands. Figure I-represents the side view of a globe, and illustrates the optical principle disclosed herein. Figure 2 repv resents a top view of the same lobe, and

indicated. In these two: figures, the same reference letters are used throughout'to define like, or similar points.

I The optical 'pmhwiple.-=-Assume that the circle shown in :Figure 1, is a section of a transparent and-perfect globe half filled with, say,mercury WL.

"C is the center ofthe globe, and the center of WLs reflecting surface; w

the position ofa horizontal line the reflected iz 'ig'o h ch forms the artificial horizon net v O and" H are positioned on opposite sides to H and the reflected image of H will be tude.

'0 -'s the 'int of observation 9 andH is of the globe, in the plane which passesthrough center G, their respective distances from C being equal. Again, 0 and H are" fixed with relation to each other, but are free to move about C through both altitudeand. azimuth.

When 0 and H are in the same truehorizontal plane, the artificial horizon plane'is indicated by OCR. I 'The dotted line through the 0 indicates the true horizontal and the angle A repref sents the angle at 0 between the true horizontal and-the artificial horizon plane; Now, as O is moved to 0 so will H move Th dotted line through '0 again indi cates the true horizontal, and as the line 0 B is seen to be parallel to OCR, the angleA" must'equal the original angle A. The angle A therefore remains constant, no matter how 0 and H move during the time of an ob? servation. Oonsequentl ,the reflected ima eof H 'ves a reference ine which is practically' xed relatively to the true horizontal.

The vertical an 1e or altitude of an visible body, sa a ove thetrue horizonta can be obtaine 1X amount of angle from the observed alti-" The angle A is therefore in the na ture of a .lconstant which must be a plied to all altitudes measured, and it will e refe'rred to later under the name of the horizon correction. Such is the optical prinine. Arrangement whereby the of ayesimply subtracting the cipl'e employed to give an artificial horizon illustrates the'method by which irection is 1' fleet ion is stabzZized.J-For use'on shore, or

where the instrument can remain in a condi tion of perfect rest, any reflecting surface which is perfectly plane and truly horizontalwould answer the required purpose;'but on,

shipboard where rolling, pitching and other" motional efl'ects are experienced, means mustbe providedto neutralize their disturbing effects on. the reflecting medium. Here it is intended to use a gyroscope, that seeming a most perfect means of stabilization. ,1

As the employment of a oscope, due to itsprecession, and the earth 5 rotatlon, neces The laws referred to are nain'ied respec-' tively, the fixity in space, and the preces-' sional law of the roscope; andto their combined action is ue the fact theta gyroscope can answer the reiglilired purpose.

a ma be de' ed as a wheel to suppeited' as to be free to-rot'ate about its spinning axis, and meantime to move about two other axes perpendicular to each other, and to the spinning axis of the wheel. A wheel so universally mounted is usually referred to as having three degrees. of freedom. A perfectly balanced. spinning mass, its centre of avity bein in coincidence with its point 0 support, w en endowed with the freedom as described, will maintain'its axzs in a fixed direction in space regardless of. the manner in which its supporting frame is moved or tilted. Thus the fixit'y in space law manifests itself; and in order to explain the performance of a gyrosco e when subjected solely to this law, the 0 lowing illustration is ven Suppose that a gyroscope is in action n, say, 60 .degflees north latitude, and is so positioned wit respect to a star in the zenith, that its axis points directly to the star. The axis of the gyroscope will then be in the true vertical, but it will not long remain so. Immediately, the western rim of the 0 wheel will be depressed below the tru li orizontal, and ,this depression move from west, throu h northwest, to north, and so on; whilst t e gyro-axis re- 40 mains fixedly v ointingto the star. A rescope arran at the commencement 0 its spin with its axis in the vertical will therefore, unless positioned at either pole'of the earth, -or' on the egliliator, appear to trace a complete circle on its axis, once in every sidereal day. Thus the iixity in space law afie'cts .the gyroscope so as to show a dail round of precession, the direction of whic is seen to be in oppos'tipn to the direction of the earths' rotation.

ailyyround ofv precession being caused by the earths rotatlon, will henceforth be.

ed the rotational precession. owto consider the two exceptions, name- 1y, when the gyro spinning at the earths and when splnmng on the equator en positioned at either pole of the earth, aggro spinning with its axis in the vertical wi continue to maintain" that position, its

7 9 axis coinciding exactly with the axis of the earth. In'this case there will be no rotational precession, and 'the'axis willremain undisturbed in the true vertical.

On the equator, the above condition is, as

55 it were, reversed. ate, the western edge e celestial concave, with eriod of twelve hours running mm consideration of the above it can be seen that, irom a navigational point of view an error will be occasioned by the rotational precession,- and that this error will be zero at the poles of the earth and of maximum ammmton'the-eqaator,

The law of precession may be made apparent by causing a forceto push perpendicularly on one end of the gyros spinning axle, when the spinni wheel will turn from its "original diiection in space, and at r ght angles ;to the direction of the applied force, with the attempt to bring its axis parallel to the new axis of rotation-by the shortest path, and so that the spin of the wheel coincides' with the direction of the applied iorce. W'ere the ap lied force madejo act on the other end 0, h the axle, the effect produced wouldbe similar, but reversed in direction.

In the foregoing statements and remarks with a view to a clear explanation of the gyroscopic laws, the gyroscope-referred to is one which is so balanced that its centre of gravity is in coincidence with its point of support. Such an instruinent would be of no practical value in navigation, as it wou-ld be almost an impossibility to know whether its axis was in the vertical, or otherwise. Therefore the gyro intended for use in this case is one which is so constrained that it will naturally seek the vertical with its axis; that is to say the centre ott rav-iqty of the. re should be positioned eit er above, or 'b ow its point of support. To have the gyros centre of gravity above its [point of su rt although correct in theory, is not .go d l in practice, as owing to sinkage of the wheel due to ordinary wear and tear, it is possible for the centre of gravity to coincide eventually with thepoint of support; in which case, the, gyro although apparently spinning to perfection would be registering an error unknown to the observer: For this reason, the gyro used -in connection with this invention will preferably have itsoentre of gravity below its point of support. 1

In the case where-a gyro so balanced has its axis displaced from the vertical by an applied force, then when the force-ls removed the gyro will immediately commence to precess, with the 'endeavour to bring its axis again into the vertical; This endeavour takes the jfo'rm of a steady precession *in the opposite direction to that in which theigyro is spinning, during which the gyro-axis traces out aspiral in space,-each winding of vertical until the gyro finally comes to a the spiral bringing the axis nearer to the so tre of rotational precession.

Y J The purpose served by the gyroscopic laws may now be defined asfollows: Whilst fixity in space serves to so stabilize the gyro that it can successfully throw oif the efl'ect of disturbing influences such as arise from the rolling, pitching, and other motions of a ship atv seat, precession tendsto-bring the axis of the gyro back into the vertical, whenever it is deflected therefrom.

Now, with respect to the earths rotational direction, it may be said that there is only one |5 correct way in which to spin the gyro, namely, such that will cause the gyros precession to take place in the same direction as that manifested by the rotational precession. This means that a gyro balanced with its cenravity below its point of support should e rotated left-handed, or against the hands of a watch, in the northern hemisphere; and right-handed in the southern hemisphere, these rotational directions being as seen when looking down upon the upper plane surface of the wheel. Under such spin-' ning conditions, a gyroscope will attain its greatest steadiness of action. I The efl'eot of the earths rotation upon the gyro balanced androtated as'intended'may now' be considered. In the first lace, the rotational precession will cause a epression of the western edge of the wheel, with the result that the gyros centre of gravity is displaced from beneath its point of support and to the eastward, when the earths' gravitational force is brought into lay in the nature of a downwardpull on t e eastern edge of the wheel. This new force will therefore ',-tend to rotate the gyro bodily about a north and south axis, and that with a'direction of spin from west to east through the upper part of the revolution; and according to the law of precession, the gyro-which we assume is spinning left-handed in the northern hemisphere-will respond by depressing the northern half of its upper plane surfacev below te true horizontal and so bring its axis of spin nearer to the new axis of rotation, and its direction of spin from west to east when looking upon the southern-which is ;the higherhalf of the wheels plane surface.

The degree to which the upper plane surface of. the gyro is" deflected from the true 5:, horizontal is actually what remains of the error caused by the rotational precession, after such error has been eliminated, as far as possible by the gyros precession. This remainder constitutes the correction for the oe earths' rotation, which must be applied to all altitudes (exce ting those of bodies hearing east or west 0? observer), and it may be named therotational correction.

Now, there is another correction which .6 must; be applied to all altitudes measured negligible amount so far as whilst the gyro itself is in a state of preces-f sion due to its axis being abnormall inclined from the vertical, and this may 7 named the precessional correction. Methods whereby t e rotational and precessional corrections can be found, and applied to an altitude, will be explained later.

There are still two further pointsto be considered in connect'on with the gyro, namely, its period ofrpre ession, and its velocity of spin. With regard to the gyros period of precession, e., the time which it takes when spinning'to make a com lete round about the vertical with its axis) t is is partly decided upon with consideration to the rolling period 0 a ship as the spinning gyro must not be so influenced as to synchronize to any appreciable extent with the ships motionsin a seaway. The work synchronize as used here, does not mean that the spinning gyro will be influenced by the rolling of a ship in the same way that .:a pendulum. would be influenced under the same conditions. In effect, if a ship rolls to starboard andso causes the upper end of the gyro-axis to incline towards her stern then, wheh she rolls to port the upper end of the yro-ax s will incline towards her head, and othm'ovements, will be in accordance with the law of precession. Now, when the gyros point of support coincides exactly with its centre of gravity, then the rolling motions of a shi can have no influence whatever on the vertlcalit'y of its axis; v but as the distance bettveen its point of support and centre of gravity is gradually in- 100 creased, so will the influence, of roll be increasingly manifested. Thus when the gyros point of support is displaced only a Very small distance away from its centre of gravity, then the inclination of axis produced 105 by the ships roll will be so small as to be a ractical navigation is concerned, and un er this condition it is intended that the gyro will be used.

A factor which may be employed as repre- 1m senting the value of the distance between the gyros point of support and its centre of gravity, is its period of precession. This eriod increases as the point of support is rought nearer to coincidence with its centre of gravity, and it also increases as the velocity of spin is increased, and vice versa.. It must be remembered, however, that observations will be required whilst the gyro may be processing, and therefore the period of precession must not be made-too longs; A period of between two and three minutes Wlll prove satisfactory so far as elfectively sta bilizing the gyro is concerned and will prove suitable with regard to the taking of observan25 tions. 1 r

When deciding u on the nature of the power to be rovide for the driving of the gyro wheel, it must be remembered that the sextant will be attached to the instrument for its observations to be taken and" consequently,

, there shouldibe no vibration present such as would detrimentallyeffect the more or less delicate adjustments of the sextant glasses. .3 Therefore, although the gyro may bearrangedto be continuously power driven, in order to obviate probable sextant errors due to Vibration it. ispreferable that the gyro shouldbe arranged to spin byenergy initially impressediupon it, that itshould" be so spun and manipulated ithatwh-en sufficient velocity of spin has-been obtained, it can be uncoupled from the driving force, and thewheel left free.

to-spinof'its-ownaccord in a suitable means rof support. The initial velocity of rotation given to the gyro should be sufiicient'to enable it to spin effectively foraperiod of say, firteen minutes, which. will be ample length of time for the takingof'any ordinary observation. w The means-where by direction is indicated.'- This method of direction indicating is explained with reference to Figure 2. In this figure, the inner circle represents the transparentglobe, as in Figure 1, with O the point wrof observation, C the center of the refiec tii lrllg surface, and H the horizontal line. artificial horizon line R'is not shown, but it is understood to lie immediately below H.

The outer graduatediportion represents a all-ring of. direction which encircles the globe, say, on a levelwith WL.

X is the position of a body which has just.-

been observed.

Then it is obvious that the vertical plane as which passes through 0, C, .H, R and X will intersect the ring of direction at the bearing of In the figure, the bearing of X is seen to be'north 39 West.

From the above. it will be seen that the reflected image of H not only forms an artificial horizon .line, but provides a line of alignment or sighting line whereby direction can be shown as here illustrated.

In the com leted instrument, it is intended that the bearing of X will be .read'from that sideO of the ring of direction which is adjacent t Description of iwstmmwnt.1t will now be explained with reference to Figures 1 and 2, how the aboye principles can be embodied in an instrument of the horizon and direction tion is used when it is desired to fix the gyro wheel so that the instrument can be safely transported overland. In the clutched position the gyro is held-so that it can be given a high velocity of spin, and then instantly released into its freely spinning position.

this apparentvibration (which causes a hazy When in the free position, the gyro is supported with its spinning point in a small hemispherical shaped cup, so that the spinning gyro can maintain its axis in its natural direction in space, regardless of how the caseis moved or inclined during the time of an observation.

The position indicated by the point H is occupied by a screen, on which is shown a I central horizontal line the reflectedimage of which line forms the artificial horizon, and with other divisional lines above and below the central line.

The point'O is the point of observation, say, at the centre of the telescope eye-piece of the attached sextant.

The points-H and O are held in position with relation to the gyro by means of suitable arms which are fitted rigidly to the case, and are equally distant from the centre of the cup shaped support of the gyro wheel. The centre of this cup is indicated in Figure 1 by the letter C, and in the instrument it is the common centre about which the suspended parts move, turn, or rotate. As the case forms the foundation or support for various important parts it is strongly constructed, and preferably is made so that it. constitutes an airtight compartment from which the internal air can be extracted, thus reducing the resistance of air on the spinning gyro and thereby considerably lengtheningits effective period'of spin. g

Suitable windows are fitted in=the upper part of the case through which the spinninggyro and the artificial horizon line can be seen.

A small spirit level, fitted to any con venient part of the case, indicates to the ob server whether the axis of the gyro wasne'ar the vertical, or otherwise, at the instant when the wheel was released from the clutchedf position to spin freely of its own accord.

Now, especially if the gyro isunevenlybalanoed about its spinning axis, or unevenly held by the clutch, it may on occasions be seen to spin with an apparent vibrative movement upon being released from its clutchedto its free position; and in order to eliminate n5 artificial horizon), suitable means may be provided inside the top of case- The case with its various attachments is held rotatable through azimuth in a set of gimbal rings, which rings'a re in turn'held in.- a suitable fork-shaped support. I

. The inner ring of the gimbals holds in posi-i tion the means for indicating direction, and on this gimbal is also shown the instruments lubber line.

The means for indicating direction takes the form of an azimuth ring or dumb compass card, in combination with the lubber line; above mentioned, and with a pointer which is fitted on to the case. The azimuth:

Patent No. 167 ,075,) may be conveniently shown, and used so as to easily convert compassbearings into true, and vice veisa,

thus obviating the risk of error so far as the conversion of bearings is concerned. In order to facilitate the rapid noting of bearings from the azimuth ring, the directions as shown on the rin are reversed in relation to the direc tion as indicated by the ships compass. That is to say, the instruments lubber line is positioned aft of its centrethus when the azimuth ring is set to correspond with a compass or true course, that course reading is shown by the ring towards the stern, and not the head of the vessel. Such arrangement permits an observer to read off the bearing of an observed object from that side of the azimuth ring which is adjacent to him. Also, numerals and the. like are so engraved on the azimuth ring as to be readable from outside the ring.

A fork-shaped support of the gimbal rings is held in a standard which is fitted on to the ships deck in a suitable position for observation purposeswith the plane of the fork in the ships fore-and-aft line. Means such as shock absorbing springs may be provided in the standard, whereby the vibrative effects of the ship are neutralized as far as possible, and the instrument can'be adj ustably held as far as height is concerned.

In order to give the gyro the necessary velocity of spin, it is preferable for a small electric motor to be provided, but if the instrument is intended for use in a ship not supplied with electrical installation then suitable mechanical or like means may be employed to spin the gyro.

A small lamp for the purpose of lighting up the horizon screen at night, may be supplied with the instrument.

In ordinary practice the azimuth ring is set to indicate the ships true course. The

' gyro is then spun, and the sextant attached,

with the axis of its telescope directed in the vertical plane through the object to be observed. By moving the index arm of the sextant the observedobject is brought into coincidence with the artificial horizon and the sextant reading noted. This reading, when corrected as will later be explained, will be the true altitude of the observed body. The

bearing of the observed object will be the reading of the azimuth ring in coincidence with the pointer at the instant of observation. Details of construction-The construction of t is example are possible and certain of these will be mentioned later in the specification. In order that the invention may be clearly understood and readily carried into effect, an embodiment will now be, described more 715 fully with reference to the accompanying drawings.

In the drawings, Figs. 1 and 2, as before stated, illustrate the principles of the in-- 'vention, Fig. 1 being a side elevation of a 8 globe illustrating the optical feature and Fig. 2a plan of the same globe illustrating the method of indicating direction.

Figure 3 is a vertical section taken throu h parts, loo H the center of the case and internal ing from front to back;

, Figure 4 is a vertical section taken through the center of the case and internal parts, looking from side to side;

Figure 5 is a horizontal section taken through the case; Figure 6 is an elevation of the case looking from the left side, toward the clutch mechanism;

Figure 7 is a plan of the instrument; Figures 8 and 9 are plan and sectional views illustrating the horizon. screen;

Figure 10 is a side elevatlon of the instrument;

.zontal section illustrating the top of the standard by which the fork is supported;

Figure 12 is a plan of the instrument, the horizon screen and sextant supporting arms being broken away; I

Figure 13 is a vertical section taken through the gimbal rings and adjacent parts; Figures 14 and 15 illustrate a modified form, Fig. 14 being a vertical section taken through the center of the case and internal 1 parts looking from front to back, and F12. 15 a like vertical section looking from 1 to right. f g All the above mentioned figures are to the same scale, with the exception of Figures 7, 10 and 11, which are. reduced. These latter mentioned figures are to a scale which is equal to 4/10 the'scale of the others. Figures 16 to 21 are diagrammatic views of a theoretical nature, and are used in ex- 1 plainingthe apparent actionv of the artificial horizon line and the formulae-employed in finding certain corrections. These figures are not drawn to any particular scale.

Finally Figure 22 illustrates a marking on the gyro surface. The terms front, back, left, right, and the like,.will beunderstood upon referring to the drawings. It will be seen that the sextant arm 28 (Fig. 7) extends over the Figure'll is a plan view and part hori- .100

' screen arm extends over the front of the instrument, and is attached to the left side -;of the case.v

Throughout the drawings, similar parts are marked with like reference numerals. It

'willabe assumed whilst describing the con-v struction, that the reflecting medium is alwafiyfiein the .true horizontal lane.

gym 1 is depicted in igures 3 and 4. It preferably consists ofthree parts, namely,

' the body, the spinning point holder, and the spinning point. The body of the gyrois' shown of partly spherical shape, with a some- :what conical opening in its bottom part. The disc-shaped spinning point holder 1 is screwed upwards into the body of theigyro at the top oi-the ccniealopening. The spinning 1 shown as 'a small screw, is firmly held screwed into the spinning point holder. The spinning point holder and the spinning point should eaoh be provided with slots for adjusting purposes; and-suitable screwdrivens for engaging in (these slots, should be provided with the instrument. The complete gyro is made :up of :the three pantsmentioned in order that when-the spinning point has become Worn and blunted it may be easily removed and replaced by a new one. The body eithe gyro should-be made ofa suitable hard and strong nonqnagnetic metal and the spinning point holder and the spinning point may be made of steel. The spinning point should *he so tempered that it combines tun ness with hardness, but :it should not be. me. hard as the cup-shaped support in which it spins. All parts must be made so that the gyro is evenly balanced about its spinning axis. The upper surface of the body-is intended toact as amirror, and therefore must be perfectly plane and highly polished. This-fine-degree-of polish may be .attwinned by eleotro plating the surface concerned or by other suitable means. It is preferable however that the whole of the plane surface of the gyro should not be polished, but that adulledor blackened portion 64 as shown in Figune 22 should appear at or nearthe edge'of the surface on one side of its centre so as to enable an observer to tell whether his '0 is spinning-at a high, or low speed. A airly high speed is essential for good observation purposes, and under such spinning conditions the dulled portion 64 of the surface will not be noticeable, but when the spinning-gyro has slowed down to such extent that its speed is in'sufiicient to ensure goud stability then the flickeringfappearanceof time light irom its polished surface, caused by the momentary appear- I Since ofthe dulled portion the eye, will intimate to the observer that his gym requires reaipinning. p

n order that the gyro may be easily rememes moved fromits case (required when changing its spinning ,point, or so as to oil the moving parts), a suitable pair of tongs-should be provided with the instrument,'the tongs be ing so shaped that they Will grip firmly on opposite sides ofthe gyro.

The gyro 1 iscontained in a strong metal case 2 which can conveniently be made in box form. As the case 2 forms the foundation of a number of important parts, it must be strongly made, and preferabl should be constructed with a view to its lieing made airtight so thatthe internal air can be extracted when required. Particular points to note inthe design of the case 2 will be understood as the other parts in connection with it are described. I

At the bottom of the case 2is a strong bean ing 3, in which a vertical spindle 4 is rotatably held.

The bearing 3 may be shaped as indicated by Figures 3 and 4, its upper end being cupshaped so as to collect any oil which may be thrown out from the rotating parts by centrifugal action, while its ldwer end is externall'y threaded and projects below the bottom of case 2. The bearing 3 when once screwed into position in-the bottom of case 2, may be soldered or otherwise permanently fixed in that position.

The upper end of the vertical spindle .4 is bored out so as to hold firmly screwed in posi- "tion a hardened steel part 5. The upper end of part 5, which forms the support of the spinning gyro, is cup shaped, the inside surface of the cup being accurately spherical and highly polished; This portion of part 5 shouldbe hardened to an extreme degree of hardness, so as to obviate wear of a material amount being caused by the spinning point of the gyro. .The centre of the cups hemispherical surface, which lies in the axis of the spindle 4, may be considered as being the common centre about which the combination of moving parts moves or rotates. Preferably,- the part 5 will be adjustably held in the vertical spindle 4. In Figures 3 and 4, it is shown screwed into the bored out part ofthe spindle 4, where it is held i-n'position by a lock nut. The spindle 4 rotates on a ball race 6 and is prevented'from moving vertically in the bearing 3 by a collar 7. As shown in Figure 4, the collar 7 is secured to the spindle 4 by a small pin 4.

' A vertically sliding clutch 8 (Figures 3, 4 and 5) has a cup-shaped head moulded to fit gyro 1 exactly, and a sleeve 8 which fits slidably on the spindle 4, on which it is splined by means of a slot and a feather 9 firmly beddedinto spindle 4.

An outer sleeve 10 fits freely but not loosely on the sleeve 8 of clutch 8, and is held there by a collar 11, which screws on to the lower end of the clutch sleeve.

A vertical feather 12 (Figures 3 and 5) is fitted on to the front outside surface of sleeve 10, and this feather is freely but not loosely held in a guide block 13. The vertical feather 12, when engaging the guide block 13, prevents thesleeve 10 from rotating, but permits it to move verticall in unison with clutch 8. Ball bearings (iiot shown in the figures) may beprovided in order to reduce the frictional resistance between the clutch 8 and sleeve 10, if desired. a

A vertical toothed rack 14, carried on the.

sleeve 10, engages with the teeth of a wheel 15 which is mounted on a horizontal spindle 16 'Figure 5) carried in bearings in the case 2. A small collar is shown pinned on to the right end of the spindle 16 by means of which the spindle is held in position at that end, and the case 2 is made airtight at this point by means of a cap 17. A (llsc-shaped part 18 is; permanently fitted on to the left end ofthc spindle 16. Surrounding the disc 18 a collar 19 is permanently fitted on to the left side of the case 2. The outside surface of this collar is provided with a left-handed screw thread, and on to this is screwed a cap 20. This cap is formed with a central circular aperture, through which the left end of the spindle 16 protrudes, and the screw rim formed on the ca is of such depth as to allow of the cap being screwed on till'its flanges part presses tightly on the disc 18.

The disc 18, collar 19, and cap 20 are intended to form a combination whereby an airtight joint can be formed at this point of the case 2, when desired. A suitable rubber or leather washer may be utilized here in order to ensure perfect airtightness. or the surfaces concerned may be'so ground that the employment of a washer is unnecessary.

As illustrated in Figure 5, the left end of spindle16 is of tapered form, and ends in a left-handed screw threaded part. On to this taper is fitted a strong milled-headed knob or handle 21 (Figures 5 and 6), and this knob is firmly held jammed on the spindle 16 by a lock nut.

Catches 22 are permanently fitted on the handle 21. These catches are so formed that they overlap the cap 20, and their ends extend towards the side of case 2.

A trigger 23, held in a casing of its own which is attached to the side of the case 2, is surrounded by a spiral spring which presses it continually outwards, and this trigger engages in turn with each of the catches 22, as

spinning point supported in the small hemispherical cup at the upper end of part 5.

In order to remove the gyro from its free to it's clutched position, turn handle 21 until the clutch catch is held by trigger 23, when the gyro will be resting in the cup-shaped part of clutch 8, and in this position its spinning point should just be free of contact with the surface of the cup of the part 5. Tommove the gyro from its clutched to its clamped position, the handle 21 is further turned until the clamp catch engages with the trigger, when the gyro will be held firmly between the clutch 8 and the top of the case 2;

To reverse the above operation it is only necessary to press the trigger 23, when the force of gravity acting upon the gyro and clutch will cause them to sink to a lower position.

Thus, the wheel 15, spindle 16, handle 21, catches 22, and trigger 23 form a combination whereby clutch 8' is operated as required, accordingly as it is desired to clamp, clutch, or permit the gyro to spin freely.

An arrangement is also provided to form an airtight joint where the spindle 4 protrudes through the bottom of the case 2. Here, as indicated in Figures 3 and 4, the ring shaped'part which projects from the bottom of the bearing 3 is provided with a right-handed screw thread on its outside surface and over this ring a cap 24 is screwed.

The cap 24 is formed with a central circular aperture through-which the lower end of the spindle 4 protrudes. The screwrim of the cap 24 is of such depth that when the cap is screwed tightly down till its flange presses on the collar 7, its rim will .not' be quite in contact with the bottom surface of.

the case 2. A suitable rubber or leathern washer may be placed between the cap 24 and the collar 7 so as to ensure perfect airtightness; or the surfaces concerned maybe so ground as to make an airtight joint by direct contact between themselves. I The lid 25 is also in the form of a discshaped cap, and screws on over a screwrim (Figures 3 and 4) on the upper surface of the case 2. A suitable washer should be providedso as to ensure airtightness at this point. The bottom surface of the lid 25 may be covered with-soft leather or other suitable material, in order to prevent scratching the polished surface of the gyro 1 when it is held in a clamped position.

In order that the reflecting surface of the gyro, and the artificial horizon line can be seen by the observer, two small windows 26 vertical at an angle of 20 degrees so as to permit the rays of light to pass perpendicuare provided, one at the front and one at the larl througethem from the .gyros polished sur acelto zobservers eye, thus avoiding nnymaterial refiactional error. The win- 'dows are held in suitable openings in which J they rest :on supporting ledges. They must lheisoacemented, or otherwise efiectivelyheld, that thezcase'2 is-alsozairtight at these points. The windows preferably should bemade of a suitable good quality glass, thesurfaces of which are perfectly plane and parallel to "each other. In Figure 7 the vertical plane wlri'chrpasses through thecommon centre of the instrument and-parallel to the right and .leftsides-of the case 2, is indicated by a dotted P line through the centre of the figure, and this plane is seen to'pass in contact with the right sides of .the windows. Surrounding the case 2, and positioned as shown by Figures 3, 4, 6, 7 and 12 is a strong .metal platform 27. This platform has its centre portion cut out to the shape of the horizontal section of the case 2. It is then .placed ortfitted over the case, and the two are rigidly attached-together. A part which .may be named .the sextant -arm 28 is illustratediin Figures 7 and 10, in

which. figuresthe-attached sextant is indicat- -ed in dotted outline. ilhe arm 28 is permanentlyattachedto the right side of the case 2, :above the platform .27, and extends over the 'baek of the case. .The length of thearm 28' musthe sufli'cient to permit of the sextant bemanmuvred as required during an obnarration without any part of it coming in 'nontact with .the .fork-sha ed supporting frame (described later). Figure the sextant arm is so shaped that 'thewmticwl plane which passes-in coincidence with the rightsides of the windows 26 and through the-common center of the instruanent will'pmthroughthe horizon lass of {he sextant between-the silvered an unsil wered-tportima'and through the-axis ofthe In Figure 10, the sextant arm is shewn raised above the horizontal at animgleithatthe sextants telescope axis towards the common centerof the instrument, forming an angle of with thetmle :lmriaontal.

As there are many designs of sextants on theunafket, the arm 28 mus'tbe' made with elueregardrto'thedesign of sextant which is eintendetl' tobe used in connectionwith the in- :It is posible thatthe arm will have to be bent or altered inashape incompaa'ieon with the form as illustrated; but whatever the of the am, it should'be snohms-toprevent undue stress 'or strain being put npomthe frame ofthe attached sextaut, and the arm as illustrated is shaped with such object in view. Here it is seen thltrthere are two horizontal grooves'or sockets formed in the arm, one groove 28 being across the back end of the arm, and the other 28" across its upper surface. The first men- -s indicated by- -of 20 with the horizontal.

tance DC.

I menus strut which connects 'the sextant hand e to itsiframe- In order to'attachthe sextant, the arm 28 is first of'all entered between the sextent handle and its frame, and theleg of the telescope collar is positioned in the groove 28 made :for it across the end of the arm. The sextant is then moved until the upper strut of its handle 'rests in the groove 28",v

formed across the upper surface of the arm, Whena small slideable bolt 29,'or other-suitable'means is employed to lock the strut,.thus

holding the sextant immovable in the arm 28.

Although the sextant telescope does. not form part of this invention, it may be mentionedthat a telescope of the blank tube type will be found suitable for the required purpose; :the point of observation being a pinhole made throughthe center of the eye-plece of the'telescope.

Another arm, which may be named the horizon screen arm 30, is ri 'dly attached to the left sid'of the case 2, a ove platform 27. This arm'i's illustrated in Figures"? and I0, and in Figure 10, it is seen to be raised above-the-horizontal at an angle of 20. The

relation to arm 30 is of such "length' that the distance between the common center and the horizontal line on screen '31, is equal to the distance between the commoncenter and the point of observation. therefore besaidto govern the length of the arm '30. I

horizon screen 31 is fitted perpendicu: larl-y. to the'outerend of the arm 30, and so The length of arm 28 may that the line which joins the central horizontal line on the screen with the common center, of the instrument will make an angle The horizon screen preferably should be made of-a zgood quality 'glassmnd bedesigned to conform to the following requirements?- The width of the horizon screen from left to right .must be such that 'whenattached permit of at least 12 degrees of arc-bein shown on its inner surface-degrees 'whic conform to a radius equal -to-the distance between the point of observation .and the common centreofthe instrument. This radius is represented in Figure 1 by .the dis- The "outer or front surface of the glass which forms the horizon screen may beperfectly plane, and shouldbe ground or du'lled so as to act as a diffuser for the light which passes through it to :thejn'ner orback surface. The inner or back surface of the screen should-be shaped so as to conform to the inside surface of a hollow cylinder, the radius of which is reipresented in Figure'l by the. distance 'OO. igure9'is a section throughthe screen, and indicates the plane and curved surfaces mentioned above. The inner curved surface preferably should be stained in two distinct colours, the division line of the colours being horizontal and dividing the screen into exactly two halves. The division line thus shown may be termed the screen horizon line, which line is indicated by H in Figures 1 and 2. Above and below the screen horizon line are-other lines which further divide the screen into equal intervals representing, say, 20 minutes of are each, in conformity with the radius which governs the curvature of the screen. The dividing of the horizon screen is illustrated by Figure 8. With reference to the marking of the diflerent divisional lines, it must be understood that they are not marked as above alluded to, but marked as if they conformed to a radius equal to the distance;

I should be shown in minutes of are only;

e. g., 10, 20, 30 and so on, up to 180 minutes on each half of the screen.' The screen horizon line is, of course, the zero point. Further, the upper half of the screen is marked with a minus sign, and the lower half with a plus. During the ,process of marking the screen 3l, it must be remembered that the screen is shown to the observer by-reflection, and in consequence is seen inverted, with the plus sign uppermost. and the minus sign lowermost. The numerals used for marking purposes are therefore engraved upside down on the screen, as illustrated by Figure 8. The divisional lines and other markings on the screen above and below the horizon line are for the purpose of facilitating the taking of observations whilst the gyro is in a state of precession (as will later be explained);

and when so arranged and marked, the hor1- zon screen really forms a complement to the are of the sextant. ;A strong metal shade (not indicated in thefigures) should be fitted so as to extend from above the front window '26, to above the horizon screen, thus shading the screen The right hand edge of this shade will terminate at the vertical plane indicated by the 05 dotted line in Figure 7.

' within easy reach of when the In order to provide the high velocity of spin required by gyro 1, it is preferable for an electric motor 32 to be used. The 'motormust be made with regard to the nature of, a

the electrical installation of the vessel which the instrument is to be used, and its speed must be sufficiently high to provide the gyro with good initial velocity of spin, preferably not less than 2000 revolutions per minute. As illustrated by Figure 10 of this example the motor is shown to operate with its spindle in the vertical, and it is intended that the direction of rotation itgives to the gyro will be left-handed in the northern hemisphere, and right-handed in the southern. In order to get these'directions of rotation, the

endof the motor spindle which rotates lefthanded (as seen when looking down upon it) y will be used uppermost in northern latitudes and lowermost'in southern latitudes. So as to obviate mistakes being made, such as driving the motor with the wrong end of its spindle uppermost, the ends of the motor casing are marked N. and S. in accordance with the direction of the spindles rotation; e. g. N. for left-handed rotation, and S. for

right-handed. These markings are indicat-* ed in Figure 10. In lieu of the above method of reversing the gyros direction of rotation, a reversing switch can be provided to the motor, in which case the respective positions of the switch should be marked N. and S. ac cording as the spindle rotates left-handed or right-handed. Preferably, an electric switch, by which the current can be switched off and on as required, should be arrangedthe observer at the inv strument.

A cage 33, which is rigidlyattached to the such manner that the motor can be easily inverted when necessary. The upper endof the 10 motor spindle'is coupled to the lower end'of the spindle 4 by a coupling '35. Both spindle ends preferably should be of the same diameter and, as shown by Figure 3, the coupling 35 is secured to thespindle ends by means of small grub screws. The coupling 35 should be of such depth from top tobottom that ub screws are released from the spindle en s the coupling can be raised over ofthe cage 33. This knob is to connect the I movable parts of the instrument to the fork-'. shaped frame (described later),'so thatthe" parts concerned are immovably held with relatlon to eachother.

. his gyro is suitably to the vertical at the mstant when he is about 13 is atta to release it from its clutched to its free position. A small plointer 37 shown in Figures 12 and c ed to the upper surface of the platform 27 adjacent to the sextant arm 28,

. valve rests.

1 air inside the pump will be expelled throu hso as to be in the vertical plane which passes through the right sides of the windows 26 andt e common centre of the instrument.

This pointer is used in con'unction with the azimuth ring, as will later e understood.

The means for extracting the internal air from the case2, may consist of a non-return valve 38 (Figure 4) in combination with an air pump of suitable make. As shown, the non-return valve consists of a vertical tube in the narrowed lower end of which a ball This vertical tube is fitted to a horizontal tube, and the horizontal tube is screwed through the case 2, its outer end projecting sufficiently far beyond the outer surface of thecase to allow the nozzle of the air pump to be securely coupled thereto. A small cap (not shown in the fi re's)"'held to the case 2 by a short length 0 chain, can be used to close the outer end of the horizontal tube when the nozzle of theair pump is unattached. The air pump (not shown in the figures may be made somewhat on the design 0 a b cycle pump, but so that its effect is the opposite. That is to say, when the handle 0' the pump is pulled out, then the pump will fill itself with air throu h its nozzle, and as the handle is pushed in, t 1e 9. small non-return valve. positioned on tie body of the pump near its nozzle end. The nozzle of the pump should be made of flexible substance, and it must be provided with suitable means whereby it can be securely coupled on to the outside end of the horizontal tube of the non-return valve 38. The non-return valve 38 prevents the air from reenterin the case 2 when once it has been drawn v om the case into the body of the air pump.

By means of the platform 27, the combination of parts hereinbefore described is supported in a gimbal ring 39 (Figures 12 and 13) in such manner as. to be freely turnable through azimuth. This gimbal is formed with a concentric groove in its upper surface,

oove the azimuth ring is ro- The lubber line-of the insruand in this tatably hel -ment is shown on the upper surface of the 'mbal ring 39; also, the course correcting 'agrams, with their-small E. and W. arrows (somewhat as in my British patent specifica:

I tion 167,075, of July 16th, 1920), may be shown in the vicinity of the lubber line.

The lubber line is indicated in Figure 12 by a thick black arrow head, and the course correct di-a rams are shown, one on either side 0 the l ubber line,

The azimuth rin 40 is meant to represent a compass car and preferably should he graduated into degrees from 0 at north and south, to on east and west. The numerals which indicate the degrees should be so en raved on the ring that they are readable fi'om outside its mm. This method of engraving the numerals is indicated by Figure 12.

The gimbal 39 is pivotably supported by means of axial screws 41, in an outer gimbal ring'42, and the gimbal 42 is in turn pivotably supported by axial screws 43, in a forkshapedframe 44 (Figures 10, 12 and 13). The point of intersection of the axial lines of the gimbals should coincide with the common centre of the instrument. This method of suspension permits the instrument to be c rated about the common centre, and thus 0 viates any displacement of the gyro when spinning, such as by a movement on the part of observer.

As shown by Figure 10, the frame 44 is is 1n order that the suspended parts can have a freedom of movement from the vertical in' the vertical plane through the frame of, say, 20 degrees, thus reventi tact between the rame an the moving parts when observations are being taken whilst the ship is pitching heavily.

- knob 45 similar in section to the knob 36, is formed on the upper surface of the bottom art of the frame 44, and on knob 45, a sli eable cou ling 46 is situated. The coupling 46 is for e purpose of holding the kno. 36 and the knob 45 firmly clamped together, thus holding the case 2 and the frame 44 immovable with relation to each other, when the apparatus is out of use. The coupling 46, although slideable vertically over the knob 45, should be permanently attached thereto, and this condition may be provided for by having a vertical slot through the knob 45 from front to back, when the coupling 46 can be attached to the knob 45 by a pin which sses from front to back of the coupling rough the slot. The vertical measurement of the slot should be such that, 20

when the coupling is raised till the pin which holds it to the knob 45 is in contact with the upper end of the slot, then one half of the coupling will be positioned over the knob 36. A milled headed clamping screw, or

.othersuitable arrangement (not shown in undesirable cou- The parts just described are held in astandard '48 (Figures and 11), which may -be made as a strong metal or wooden cylinder of any suitable diameter. This cylinder should have a flanged lower end by which it can be bolted securely to the ships deck;

and when bolted to the deck, the centre line of the cylinder should be in, or near the vertical when the ship is upright and in good trim.

The leg 47 is supported in the standard 48 by means of two platforms 49. One of these platforms is positioned at the top of the standard 48 as indicated in Figure 11; and

the other is positioned inside the standard, about one foot from the top. The platforms may consist'eachof a disc-shaped piece of metal of suitable thickness, the centre portion of which iscut out to conform with the horizontal section of the leg 47, so as to allow the leg being freely but not loosely held in these openings. Both plat orms may be held in position in the standard 48 by means of spiral springs the object of these springs being to minimize the effect of jar or concussion caused to the instrument by the heavy plunging of the ship, or by her vibration. The upper platform 49 is provided with vertical lugs 51, and each of these lugs is provided with axhorizontal left-toright hole oppositely positioned to each other. The diameter of these holes conforms t5; the diameter of the holes through the leg '4 t 1 The instrument when adjusted to a certain height is kept at that height by means ;of a bolt 52, which passes through the holes in both lugs and leg, when the holes concerned are in alignment with each other. The bolt 52 may be attached to the platform by a short length of chain. Now, say that the vertical distance between the point of observation and the level of the bottom of the frame 44 is 1 foot 10 inches; then if the height of the standard 48 is 2 feet 9 inchesfrom the ships deck, the instrument will be found adjustable to suitobservers varying between 5 and 6 feet in height, which will be a good estimate to work upon as far as the height of an observer is concerned. I

The instrument as described should be placed on' the ships navigation bridge in a suitable position for observation purposes, with the plane through the frame 44 in the fore-and-aft plane of the ship, and with the lubber line towards the ships stern.

Now, especially the gyro 1 is unevenly balanced about its spinnin axis, or if it rests unevenly in clutch 8, it w1ll on occasions be seen to spin with an apparent vibrative move ment upon being released from its clutched to its free position. In reality, this movement has nothing to do with vibration, but is simply 7 due to the fact that the gyro is spinning about an axis which is not perpendicular to its plane polished surface, and the result is that a' hazy artificial horizon line is shown to observer. In'order to overcome this appar- 'ent spinning defect it is preferable that suitable means should be provided. In the exexample illustrated (Figure 3) this means is in the form of a fine. spring steel wire 53, which is positioned on theright of the front window 26. Two, or more of these wires, p'ositioned opposite to each other may be provided if desired, and their spring and flexibility should be such as to ermit of them bending out of the way of t e gyro as it is being raised to the clamped position and immediately to spring out into their original form when free to do so. Then, to cause the spinning gyro to rotate about an axis which is perpendicular to its plane surface, it is only necessary to incline thecase 2 so that the wire 53 is brought in contact with the'upper planesurface of the gyro when the vibrative eifect will gradually become less and less, until a perfectly clear artificial horizon line is shown maybe provided with the instrument for use I on occasions when observations are being taken at night time. This lamp should be arranged to fit in front of the horizon screen 31, so that the rays of light from the lamp will pass through the ground surface of the screen and illuminate the raduated surface with an even diffused lig t. The sextant shades can be used in the ordinary way to regulate the intensityof the'light as required.

The complete instrument above described and as shown in the figures may be modified in detail and in design. For example, the instrument as already explained can be so modified that the clamped position of the gyro is done away with. To have the gyro so arranged that it can be held in a clamped position would undoubtedly be of service were the instrument used on aircraft, but for conditions experienced on seagoing vessels the clamped position would seldom be required.

The gyro wheel itself can be suitable altered in shape. It may be so altered that its centre ofgravity is positioned low, in comparison comparison, it maybe so altered that its circle of rotation is of greater diameter.

spond toca greater radius, say, a radius which is equal to the distance between the centre of the 'gyros reflecting surface and its point of support.

' Instead of being driven by an electric mo-.

tor, the gyro may be driven by an arrangement of geared wheels, or by other suitable means. Also, the gyro can be provided with means whereby it may be continuously power driven dnringthe timeof an observation.

Further, the frame 44, instead of being held in-standa'rd 48 as described, may be provided with suitable legs of its own, in which case the instrument would be of portable nature.

Also, certain parts may be omitted from the instrument as described, such as the spirit level and the'airtightening parts.

A modified arrangement is here described with reference to Figures 14 and 15.: Generallygin this arrangement, instead of the reflecting medium being the upper plane surface of the gyro, it consists of a disc shaped piece of metal-the 'uppersurface of which is plane and polished-suspended in agimbal ring (or-series of rings) inside the case 2; This disc is so stabilized by a gyro that i it will tend to come to rest with its reflecting surface in the horizontal. Provision is made whereby the: recessional period of the yro maybe broug t within workable limits say, within 2 or 3 minutes duration) and so that the weight of the-disc and attached parts may be suitably and evenly disposed about the line'of'the spinning axis of the gyro wheel.

In this modification the case 2 is constructed somewhat similarly to that already de- 0 parts, the upper part, which'bears the sextant scribed. Preferably it is made up in two arm 28 and the horizon screen arm 30, being removably fitted on the platform 27.

As shown in Figure 15 theupper part of case 2 is provided with lugs through which screws are screwed to make the attachment with the platform. The case 2. is provided with V-shaped sockets 54 and a gimbal ring 55 is supported by knife-edged points of suspension in sockets 54, preferably on -a leftto-ri ht axis. The gimbal ring, in turn, is provided with similar V-sha-ped sockets 56, and a disc-57 is supported on a front-to-back axis in the sockets 56. 3

Surrounding the disc 57, in the vertical plane through its left-to-right axis, is a cage 58. The-cage 58 is provided with a vertical screw 59, and the gyro 1 is carried upon a ball bearing 60 screwed into the bottom part of-the cage. The upper end of the gyro axle is sup orted by a suitable bearing fitted on to the ower surface-of the disc 57. The lower end of the. re axle protrudes through below the bearm 60, and this endis shaped with flattened sides so as to engage for drivaura-no ing purposes into a suitable opening formed in the top of the clutch 8. The clutch 8 and sleeve 10 are modified in shape as shown, and as their weight may not be suflicient to ensure prompt disen agement from the gyro axle immediately t e trigger 23 is released from the catch 22 (trigger and catch notindicated in these figures), small sprin s 61 may be rovided to create suflicient ownward pul to ensure the desired efiect. A weight 62 is shown screwed on the screw 59. The purpose of the weight 62 isto raise'the centre of gravity of the disc and attached parts, and so neutralize to a workable degree the efiect of the preponderance of lower weight caused by the gyro wheelbeing fitted underneath the disc. By using a heavier (or lighter) weight 62, the gyros period of precession can be made longer (or shorter) in duration.

Instead of being shaped as shown in Fig ures 14 and 15, the cage 58 may be formed in theshape of a small dome supported by four equi-distant legs upon the upper surface of the disc 57, and these legs should be so fitted to the disc that the vertical planes through them lie diagonally to the vertical planes through the points of suspension. This method will equally distribute the weight of the disc and attached parts evenly about the spinning axis of the gyro; and in this modification, the ro can be held in a casin of its own fitte underneath on to the disc 5 Generally, the gimbal ring 55 should be made as light as possible consistent with strength, and preferably should be suspended so that in itself, it will have no tendency to swing, that is, its centre of gravity should lie in the line through its points 0 suspension. The centre of gravity of the suspended parts is intended to lie below the common centre of, the instrument. The centre of the reflecting'surface may also lie in the comtion of the lines through the axial screws 41 and 43.

The principle and method of arrangement just described will be found suitable when it is desired to provide a gyro which is continuously power driven. In this method all parts of the .instrument (with the exception of the case 2, its gyro and gyro-equipment) may be arranged as already shown. In lieu of the box-shaped case, the case 2 may be of' globular or bowl shape, its lower portion being fitted rigidly to the platform 27, and the turn, carries the disc shaped reflecting surface-on a front-to-back axis. Attached to the lower surface of the reflecting disc is the casing of an electrically driven gyro wheel with vertical spinning axis; and the current for driving'the gyro wheel may be led in through the bowl shaped case, and along the points of suspension and gimbal ring, until it passes to the motor so as not to create tension' or drag 'suchas might interfere with the gyro in its precessional oscillations.

In lieu of the knife edged points of suspension, such as are alluded to, ball bearing or other suitable means of suspension may be em "loyed with this instrument.

- aving now described the arrangement and combination'of parts which form the complete instrument, the following instructions'are intended to guide in its working To spin the gyra-When the instrument is fitted with an electric motor for spinning and with a gyro of the kind meant to s m by velocity initially impressed upon it, rst of all see. that ca' 20 and cap 24 are free "of contact with t e collars 18 and 7, respectively. Case 2 and frame 44 may be disconnecte'd from each other where held by coupling 46. Then place the gyro in its clutched position, and start the motor 32'. Mlow the motor to attain its maximum speed; then press trigger 23, and so release the gyro to when 1t -'1 s required to change a compass spin freely of its own accordin its cupshaped support. The position of the bubble in'the spirlt level at the instant of pressing the trigger will indicate approximately to the observer whether the ro-axis is near the vertical, or otherwise. on release of the gyro, the motor is stoppe ,land caps 20 and 24 are screwed up ti ht so as to transform the case 2 into an airtlght compartment.

- The internal air may then be extracted from the old spinning the case by means of the air. pump. On at taching the sextant, the instrument is then in readiness for observation purposes. 1 The workin parts 01' the instrument should, of course, ve kept well oiled. i To cltaage' the spa My point of the gyro.After having spun for some time it may ht sideways vibration. This vibration is due to-the spinning point having become worn and blunted, and'it is then advisable to replace do this: unscrew lid 25, and remove the ro from the case by the specialtongs provi ed. Then' unscrew the inning 'point "holder, and change the spinning po nt Make sure that the new spinning point is firml screwed into the spinning point holder, an that the spinning point holder is in turn firmlyscrewed into the bddy of gyro, before again replacing the gyro into the case. When the rofhas been replaced, then screw on lid 25 m away which'will ensure the desired airtight'connection. 4

point by a new one. To

vertical plane of direction. In this case, the; sextant is slu'ed around until the pointer 37 is in coincidence with the azimuth ring reading which indicates the required direction; when the axis of the sextant telescope will be properly positioned.

To use the course correcting diagrams.-

To change a true course into a compass course use'diagram True to compass as'follows; Rotate the azimuth ring 40 until the true course readin is in coincidence with the lubber line. T en, if the compass error is'easterly (or westerly) turn the ring 40 in the direction indicated by the small E. arrow (or W arrow) until'the amount of the error has been allowed for. The azimuth ring reading thenin coincidence with the lubber line will be the compass course re-' quired. I a

' Diagram Compass to true is similarly used course into a true course.

Previousto explaining the various altitude corrections, and so asto make the reader conversant with terms and the like which will be used in those explanations, the following definitions are now given The visible hom'eon.-The visible horizon is the natural horizon as seen at seathat point where the sea and sky appear to meet.

The sensz'bZe h0rz'z m.The sensible hori- Zen is the horizontal plane through the observers eye, at right angles to the vertical.

Dip of the sea'horz'eonr-The angle at the observers eye between the visible and sensible horizon planes is termed Dip'.

The artific al horizon later-The artificial horizon 1 through the pointo'f 'observation and ane is the p ane which asses the artificial horizon 'lt, as shown in Figj'In thisspecificationitis assumed that the v artificial horizon plane is depressed" 20 be lowflthe sensible horizon.

The (artificial h'on'zon central horizontal line on screen 31. The" term Artificial horizon'li he will be used in the e lanations to 1 follow whenever it is to be un erstood that the artificial horizon llne is not at rest in its correct position in the artificial horizon plane---e. the artificial horizon line is not at rest 'w on the gyro is I prime verticals-The prime-vertical is the vertical. lane which passes-through. the true east and west points of the horizon.

Z'he precessional COWGUtiO'Rr-WhilSt taking an observation. with the aid of this invention, the re w-illbe spinning under one at two conditions, namely, inthe processing condition, or in a condition: of a parent rest. The precessing' condition. call 1: acorrection to be applied to the sextant reading in order to reduce,- as it were,.the artificial horizon line to. its. true position in the artificial horizonplane; In, the condition of apparent rest, there is no such correction necessary; the artificial. horizon linehavin then found its true. position in thearticia-l horizon plane.

It has already been. pointed out that during. precession. the axis of the gyro traces out a spiral path in. space, and that in each siiccessive layer of the spiral; the axis nears the. vertical. The centre about which the axis turns.- spirally isthegyro s spinning pointof support; and. were the spiral ath of the axis plotted about the ole of a sp ere, it would appear asa rh curve (1. e., a curve intersecting! all. meridians on the s here at the same angle), gradually nearing t e pole at a rate which is proportionate to the length of the successive la ers of the curve. To an observer, the gyro s precession is hrought into evidence b the apparent movement of the artificial horizon line, which also traces out. a. s iral path in strict accordance with at of the ro-axis. The centre about which. the artificml horizom appears to move spiraill may beconsidered as being the centre 0- the gyrols refleeting; surfiace.

Now, the artificial horizon line whilst traci'nf. out its spiral path appears to incline itse f in succession, from, towards, and in the true horizontal At the highest and lowest turning points of the path, the artificial horizon lme will be perfectly horizontal; but from these points it will incline. graduallyfrom that horizontal position asit proceeds, until it reaches its maximum degree of inclinat'i'on whenhalfway between the two oints. This will be better. understood with re erence to Figure 16.. In.Figr1 re.l6,,the curved ABC arrow represents the apparent path ofthe artificial horizon line and. thesmall lines radiatin from. the arrow indicate the inclination 0 the artificial. horizon line at suc'ces sive points in its path. At. A, the artificial horizon line perfectly horizontal; but as it proceeds. on. its course it gradually inclines from. the true horizontal, until when half way between A. and E the maximum degree of. inclination is. reached. From there, the artificial horizon line begins to right itself, so-thnt-when atB, it is again perfectly horizontal... Asimil'ar action continues between B and C, and so on, until the gyro finally attime tainsits spinningcondition of apparent red,

when the artificial. horizon: line up ears stafinding the amount of the precessional. correctiou- In Figure 17,. O is. the point of observation or the. observers: eye-at. the centre of the sextant telescope eyeiece.

indicates the sensible horizon; an OR the artificial horizon plane. X is the position of a star to be observed. The. dotted. circle through A and D indicates the path of the artificial horizon! line were it perfectly cireular; and. the curved ABC arrow indicates that pathas itlisreally found in practice.

- Then, considering the: first case, where the path is assumed to be perfectly circular, in order to fi-ndthe precessional correctionwhich is the semi-diameter of. the dotted circ1e,. or theangl'e AORthe following simple formula will suflice I AOX DOX the precessional correction.

Then, thealtitude of X above the artificial horizon plane equals: AUX-AGE, or

DOX-HDOR. ACE and DOE are, of

course, equal to each other; and therefore indi'vidual'l'y represent the semi-diameter of the circle through A and D: Thus it is seen that the precessional correction may be an additive, or a subtractive quantity.

But, the artificial horizons path is spiral, and not circular. Therefore, in' order to find the precessional correction in practice, a somewhat different formula must be .used. As already pointed out when comparing the path of the gyro-axis to a rhumb curve on a 1 sphere, the artificial horizon. line nears its true plane OR at a rate proportionate as the successive layers of itscurved path are in proportion to each other, and] therefore,

d AOB+ BOO 'Aoo: AOB BOD an a I s non-gran =AOR recessionalcorrection can. be

the precessional correction.

The above formulamay be used directly for finding AR when the observed body iS fixed with regard to the position of the observerthe visible horizon may be quoted as an example of a body so fixed.

With the object of clearly explaining the finding of the precessional correction, and I figure represents the reflected image of screen 31, as seen by the observer through the sextant telescope. The central line on the screen is the artificial horizon line, and the other divisional lines are shown above and below it. The plus and minus signs on the screen are used to distinguish the divisional lines above the artificial horizon line, from the divisional lines below it.

In practice,the sextants index arm'is moved until the observed objects image is shown in the sextant horizon glass, near, or in coincidence with, the assumed position of the artificial horizon plane. The sextants' index arm is then clamped; and as the artificial horizon line reaches point A in its path, final contact is made between the observed objects image and the nearest divisional line on the screen by using the sextants tangent screw.

No further adjustment to the sextant is necessary throughout .the observation.

Due to the gyros precession, the reflected screen will appear to move behind the observed objects image, with the result that a difierent divisional line will be in coincidence with that image as the A, B, and

arrow ABC represents the amount of movement of the reflected screen, as described by the image of the observed object during the time of the observation; and it is seen that the image is in coincidence with plus 80 at A, with minus at B, and with plus 50 at G. Then, in order to get the amount of the angular measurement AB and BC,as required by the formula, the screen reading at. point A is added to the reading at point B, for the value of the side AB; andthe reading at point B is added to the reading at point C, for the value of the side'BC. Therefore, AB=+60=14O;

'' and BC=60+50=110.

Then to find the precessional correction AR: I

- AB+BC 140+110 --250 78.4 minutes of arc.

' and the artificial horizon line at point A When correcting an altitude for the gyros precession, the following rules are always observed 2-- I Rule 1. Apply the tant reading:

(a) Add when the A reading is plus,

' Subtract when the A reading is minus.

Rule 2. Apply the processional correction R o ((1) Add when the A reading is below the B reading on the screen (6) Subtract when the A reading is above the B reading on the screen.

In this example, assuming that the sextant reading is 40 degrees of arc, then the altitude is corrected for the gyros precession as shown below S'extant reading, or altitude- 40 0 A reading (as per Rule 1) 1 2O 41 20 AR (as'per Rule 2) 7 1' 18.4 Then the corrected altitude is 40 1.6

In the above example, the screen readings are additive in order to get the value of the AB and BC sides of the path. Had the 'A reading and the B reading been both plus, or both minus, then their difierence would have given the required angular measurement AB, and so on. 1 7

The application of the A reading to the sextant reading has the effect of altering the sextant reading to what it would have been, had, in the first'place, direct contact been made between the observed objects image in the path.

Similarly, the application of AR to the sextaut reading when corrected for the amount. of reading A, has the effect of giving the correct angular measurement between the observed objects image and the artificial horizon plane.

-The above problem and corresponding explanations should prove sufiicient to show the method of finding the precessional correction AR, and the rules which govern the correction of an altitude of the gyros own pre- A reading to the sexits cessi'on. But, it must be understood that each and every problem may vary in comparison wit each other inasmuch as the screen readings Wlll be different on almost every occasion.- This-will be explained by two further examples Ewamp'le 2.-'This example will be explained with reference to Figure 19. As represented by the figure, the A reading is the Example 3.This example will be exphi-nod with reference to Figure 20. In this example, as the 'A reading is zero, there is meaning of this specification) then a slightly different procedure must be observed in the findin ofthe precessional correction AR. This Ifi'erence in procedure is due to the retation of the earth on itsaxis, which gives to all heavenly bodies an apparent movement in space of their own as time goes on; and in consequence, the AB and BC sides of the artificial horizons path are more or less distorted or altered out of their natural shape, due to the apparent movement of the observed body during the time of the observation. If the side AB. is lengthened (or shortened) during the interval of time of the artificial horizons passage from A to B, then the side BC will be shortened (or lengthened) in accordance with the interval of time which has elapsed during the horizons passage from B to C. The chrononieter times are noted at points A, B, and C in the'artificial horizons path; thus the intervals referred to above are made known when a moving body is observed.

From what has now been said it will be seen that the AB and BC sides of the artificial horizons path must be individually treated for distortion, previous to-the precessional correction being found.

sons to simplify the fin ling of the change in altitude of the observed body (which is the first requirement in the treatment of the sides of the path), a table which shows the rate of change in altitude, per second of. time accompanies the specification. The variousrates are shown, each rate as the decimal part of a minute of arc.

To use the table and thence correct the sidesof the path, proceed as follows 2-- Enter the table with the latitude of observer at the top, and the azimuth of the observed body in the left hand side column, then note the rate of change in altitude.

This rate is found in thelatitude column, inline with the azimuth. For example: in latitude 40, azimuth 30, the rate of change in altitude, per second or time is seen tobe .096.

Then, in order to know the actual amount of change in altitude which must be applied to the AB and BC sides of the artificial horizons path, the rate selected from the table is multiplied by the interval of time AB, and again by the time BC (both times being Subtract the time BC result from the side 130.

(b) When A is shown below B on the horizon screen, and the star is east of observer; Subtract the time side AB. Adfad;C the time BC result to the side AB result mm the When A is shown above B on the horizon screen, and the star is west of observer:"

Subtract the time AB result from the side AB.

Agi-cthe time BC result to the side (d) When A is shown below B on the horizon screen, and the star is west of observer:

A XlBthe time AB result to the side Subtract the time BC result from the side BC.

When the sides-of the artificial horizons path are corrected as above directed, the precessional correction is found by using the original tormula given above. Strictly speaking there is a small change in altitude due to the 'ships own movement during the time of an observation; but this change is negligible in practice.

When the spinning gyro is released from clutch 8 with its axis near the vertical, it

will quickly find itsresting or sleeping condition with its reflecting surfiaoe plane apparently fixed relatively to the sensible horizon. In this spinning condition it is only necessary when taking an observation to there is no precessiona-l correction to find and But, a warning may be given here, for to take an observation with the spinning gyro. in a resting condition, although an easy operation,is not devoid of risk,as an error may be registered due to a'sli-ght precession which cannot well be noticed by an observer. Therefore, in order to minimize and distribute any such error, the mean of two or more observations should be taken when the gyro is sp'?;1eing in a condition of apparent rest.

omzon correction-What is termed the horizon correction "is indicated by the angle' A in Figure 1. This correction may be defined as being the angle at the point of observation between the sensible horizon and the artificial horizon plane, this angle being measured in the prime vertical where it cannot be combined with the rotational correction.

To find the angle in practice, proceed as follows :Set the azimuth ring 40 to indicate true direction, and position the sextant with its telescope axis pointing east or west. The visible horizons image is then brought in contact with the nearest divisional line on the screen as the artificial horizon line reaches point A in its path and the points A,

'B and Care carefully noted. The precessional correction is then computed and applied to the sextant reading in the way already exon the equator. r

The effect of the earths rotation on the plained. This corrected reading is the an le between the visible horizon and the artificlal horizon planes. The dip of the sea horizon (given in all nautical tables) is then added Y to the angle as above, and the sum of the" twois the horizon correction required.

' When the horizon correction is once found, it is of a fixed amount (providing, of course that the distance between the gyros point of supportand .its centre of gravity is not altered),-'and is always subtractive from the observed altitudes of bodies which are above the sensible horizon.

The rotational correction-An explanation of the rotational correction will now be given, with reference to Fi re 21. Figure 21 represents the earth, WE iieiing the plane of the equator'and NS the meridian,'or the axis of the earth. The rotation of the earth is from W to E (assuming W to be movin towards, and E away from the reader). is the position of the gyro when it was started spinning-with its axis parallel to the axis NSQ, the earth. Its position on the meridian is, say 60 north-latitude. After a period of six hours-has elapsed, due to the earths rotation, the gyro w1ll then be positioned at J; and assuming that it is uninfluenced b ravity, its axiswill then lie in the line J ow, as MK (the measurement, as it were, of the lower end of the gyro-axis from the centre M of the earth) is seen to equal the cosine of angle J ME (the latitude), it may be said that the inclination of'the gyro-axis from the vertical, due to the rotation of the earth, varies as the cosine of latitude from zeroat the poles of the earth to its maximum neutrally balanced gyro'having now been explained, assume that the gyro is so bal-' point of support. In this case, the spinning gyro will have a continual tendency to bring its axis into the vertical, and will have a short period of precession of its own, say, two minutes. The gyro is nowacting under two influences, namely, its own period of precession (say, 2 ,minutes), which is correcare aimed that itscentr'e of gravity is. belowflits.

tive, and the rotational period of precession (approximately 23 hours 56 minutes) which tends to deflectthe gyro-axis from the vertical. As far'as practicexis concerned, these two periods are operating at right angles to each other, and-for the purpose here required, they may be considered as the adjacent sides of a parallelogram of forces. In Figure 21, if J M is assumed to indicate the amount of the rotational period of precession, and PM the gyros period of precession, then the resultant of these two periods will be as indicated by the dotted l1ne JP; and the angle PJ M will be the angle of. inclination of thegyro-axis to the vertical, knowledge of which is re uired.

' Theangle 0 inclination may therefore be found in the following manner Ill-2% tangent Now, angle PJM actually represents the maximum amount of the rotational correction when the gyro isspinning on the equator, where the cosine of latitude is 1; therefore, in other latitudes the maximum amount of the rotational correction may be found by. means of the formula: Tangent rotational correction=l p g cosine latitude.-

As previously explained, the sp inning gyro is so affected by the rotation of the earth, that its upper plane surface is inclined from the horizontal; and so is intersected by the true horizontal plane on an eastand west line;

which means that the rotational correction must also vary according to direction, and in order to explain the rule which governs this variation, Figure 21 will again be con sulted. In the figure, Xis the position of a star,

and NNX its azimuth north 30 west. 1

Again, Y is the position of another star, the azlmuth of which is north 60 'west. The

cosines of these azimuths, respectively, are

XV'and- YT. 7 Knowing that the up er end of the gyro-axis is drawn towards t e pole of the hemis here in which thegyro is spinning, and t at the true horizontal plane passes through the upper plane surface of the gyro wheel, 1t is then obvious that the error,

caused by the earths rotation iszero on east and west, and is of maximum amount on north and south. This variation sseen to agree 

